The control of noise and vibration in composite structures is an important area of current research in aerospace, automotive and other industries. For example, spacecraft vibrations initiated by attitude adjusting thrusters, motors and thermally induced stresses inhibit accurate aiming of antennas and other equipment carried by the craft. Such vibrations can cause severe damage to the craft and its associated equipment. Fatigue failure of structural components can occur at stresses well below static load limits.
Composite materials have been used to construct a wide variety of structural elements, including tubes, enclosures, beams, plates and irregular shapes. Objects as diverse as rocket motor housings and sporting goods, notably golf club shafts, skis, archery arrows, vaulting poles and tennis rackets have been structured from composite materials. While composite constructions have offered many significant advantages, such as excellent strength and stiffness properties, together with lightness and chemical resistance, the poor vibration damping properties of such construction have been of concern.
The invention relates to fiber reinforced composite structures and applications that use wavy fiber patterns in the plane of the laminate, and that increase damping with little or no sacrifice in strength.
The present invention relates to fiber reinforced resin matrix composites, and more particularly, to improved crossply laminate structures made from wavy composite materials. Such materials and structures made from wavy composites have enhanced structural properties and represent a greatly enhanced method of manufacturing crossply laminates.
The present invention relates to fiber reinforced resin matrix composites, and more particularly, to improved tubular wavy composite based laminate structures with high damping, and improved torsional properties. The present invention relates to a generalized tubular wavy composite structure that is easier to manufacture, and can be used to create high quality, high capability, golf club shafts, baseball bats, automotive drive shafts, helicopter drive shafts, fishing rods, oil drilling pipe, and other tubular or structural members where damping, stiffness, and strength are important.
The present invention relates to fiber reinforced resin matrix composites, and more particularly, to improved wavy composite based laminate plates and other structures with high damping, and improved torsional properties. The present invention relates to a generalized wavy composite laminate structure that is easier to manufacture, and can be used to create high quality, high capability, panels, skis, snowboards, wing skins, fuselage components, and other structural members where damping, stiffness, and strength are important.
The following terms used herein will be understood to have their ordinary dictionary meaning as follows:
Composite:made up of distinct parts. In the general sense, refers to any fiberreinforced material but especially any cured fiber reinforcedmatrix structure.Crossply, crossply lay-up, or crossply laminate:Two or more laminae made from unidirectional pre-pregarranged in such a manner that the primary direction of the fiberor strong material direction in the layers differ in orientation, or“cross” each other.Fiber:a thread or a structure or object resembling a thread. A slenderand greatly elongated natural or synthetic filament. (Includesmetal fibers)Lamina(te):a thin plate . . . : layer(s)Matrix:material in which something is enclosed or embedded.Offset:In the context of this invention, means a generalized lead or lagof one waveform relative to another, similar to a phase angle inelectronic engineering.Off-axis:In the context of this invention, means a rotational difference ofthe strong axis between one laminae waveform relative toanother or some reference.Pre-preg:Fiber reinforced, resin matrix impregnated materials where thematrix is partially cured and ready for use. A special “uncured”case of the more general term “Composite”.Resin:an uncured binder, especially an uncured polymer binder ormatrix used to bind fibers or fibrous materials; the matrixcomponent of an uncured pre-preg.Viscoelastic:having appreciable and conjoint viscous and elastic properties.Note: a special case of the term “viscoelastic” is “anisotropicviscoelastic”, which is a viscoelastic material reinforced withfibers that give the material anisotropic properties. When theterm viscoelastic is used in the text it should be construed toencompass this special case.Wavy:The pattern of fiber lay that has a sinusoidal look, especially asinuous wavy fiber in the plain of a laminate; the wave patternneed not be periodic or uniform.Wavy composite, Wavy prepreg:defines any fiber-matrix combination having at least one fiberwithout a break (or interruption) and having a pattern which canbe defined by a mathematical algorithm. It generally has a wavyappearance. It can consist of “unidirectional” fibers (although inthis case the fibers would be placed in a wavy pattern) or wovencloth (which also will have a wavy pattern to the warp or weftand substantially straight fill fibers). This definition includes theuse of substantially straight fibers that are arranged generallyperpendicular to the generalized lay of the sinuous fibers andspecifically includes a woven cloth were the warp fibers aresinuous and the fill fibers are straight and substantiallyperpendicular. Of course were the angle of the sinuous fiberdeviates from zero degrees (to the generalized lay) the anglebetween sinuous warp fibers and straight fill fibers will not beexactly perpendicular.Wavy crossply, wavy crossply lay-up, or wavy crossply laminate:Two or more wavy fiber laminae arranged in such a manner thatthe primary direction of the fiber or strong material direction inthe layers differ in orientation.CWCV:(Continuous Wave Composite Viscoelastic) defines acombination of wavy composite and viscoelastic materialsdesigned to induce damping in a structure.CWC-AV:(Anisotropic Viscoelastic) defines a viscoelastic material ormatrix with an embedded wavy fiber pattern. Such a materialwould have anisotropic, elastic, and viscoelastic properties. It isa special case of both CWC laminates and “viscoelastic” and canbe used in conjunction with conventional CWC fiber-matrixcombinations to provide damping and unique structuralproperties. Any use of “CWC” or “viscoelastic” in the followingtext can be construed to encompass this special case.
One of the simplest and often very effective passive damping treatments involves the use of thermo-viscoelastic (TVE) materials. These materials, represented by Avery-Dennison's FT series (FT-1191 is one example), exhibit both elastic and dissipative qualities which make them useful in a number of passive damping treatments.
Co-cured composite-viscoelastic structures are formed when layers of uncured fiber composites and TVE (thermal-viscoelastic or viscoelastic) materials are alternately stacked and cured together in an oven. Damping occurs in these structures when a load causes differential movement of the opposing laminates, causing shearing in the sandwiched viscoelastic material. The various methods that use this concept of differential shearing of the viscoelastic material can be classified by the fiber orientation methods used to induce damping in the TVE material.
Conventional angled ply composite designs use ±θ lay-ups of straight fiber pre-preg materials to encase the viscoelastic layers, and were first proposed by Barrett (1989) in a design for damped composite tubular components. Barrett combined the concepts of constrained layer damping with anisotropic shear coupling in the constraining composite layers to create a tube that achieved both high damping and high axial stiffness. Barrett's research showed that maximum shearing was experienced at the ends of the tubes and that clamping the constraining layers of the tube at the ends eliminated much of the damping effect, rendering the design impractical for most applications.
Chevron patterned designs also use conventional angled ply (±θ) composite lay-ups of straight fibers but vary the fiber orientation several times throughout the structure in a given laminate. Called SCAD (Stress Coupled Activated Damping), it was first proposed by Benjamin Dolgin of NASA and implemented by Olcott et al. (1991a).
In Olcott's implementation of Dolgin's design, each composite layer is comprised of multiple plies of pre-preg composite material arranged in a series of chevron-like patterns. Each composite layer is also comprised of several “segments” of material where the fiber angle in a given segment is oriented in a single direction throughout its thickness. Segments on opposite sides of the embedded viscoelastic material have the opposite angular orientation. At least two adjacent segments in a given composite layer are required to form a chevron and are joined together by staggering and overlapping the pre-preg plies in the segment.
By tailoring the fiber angle, thickness, and segment lengths, significant shearing in the viscoelastic layer was observed over the entire structure, not just at the ends as in Barrett's design (Olcott et al., 1991b; Olcott, 1992).
The following publications, incorporated herein by reference, are cited for further details on this subject.    1. Cabales, Raymund S.; Kosmatka, John B.; Belknap, Frank M., “Golf shaft for controlling passive vibrations,” 1999, U.S. Pat. No. 5,928,090.    2. Cabales, Raymund S.; Kosmatka, John B.; Belknap, Frank M., “Golf shaft for controlling passive vibrations,” 2000, U.S. Pat. No. 6,155,932.    3. Dolgin, Benjamin P., “Composite Passive Damping Struts for Large Precision Structures,” 1990, U.S. Pat. No. 5,203,435.    4. Dolgin, Benjamin P., “Composite Struts Would Damp Vibrations,” NASA Technical Briefs, 1991, Vol. 15, Issue 4, p. 79.    5. Easton, James L.; Filice, Gary W.; Souders, Roger; Teixeira, Charles, “Tubular metal ball bat internally reinforced with fiber composite,” 1994, U.S. Pat. No. 5,364,905.    6. Hyer, M. W. (1997). “Stress Analysis of Fiber-Reinforced Composite Materials,” The McGraw-Hill Companies, Inc.    7. Lewark, Blaise A., “Reinforced baseball bat,” 2000, U.S. Pat. No. 6,036,610.    8. Mellor, J. F. (1997). “Development and Evaluation of Continuous Zig-zag Composite Damping Material in Constrained Layer Damping,” Masters Thesis, Provo, Utah, Brigham Young University.    9. Olcott, D. D., (1992). “Improved Damping in Composite Structures Through Stress Coupling, Co-Cured Damping Layers, and Segmented Stiffness Layers,” Ph.D. Thesis, Provo, Utah, Brigham Young University.    10. Pratt, W. F. (1998). “Damped Composite Applications and Structures Using Wavy Composite Patterns,” Patent Application 60/027,975. US & PCT.    11. Pratt, W. F. (1999). “Patterned Fiber Composites, Process, Characterization, and Damping Performance,” Ph.D. Dissertation. Provo, Utah, Brigham Young University, 195 pgs. (Note: not publicly released as of 1 Dec. 2000).    12. Pratt, W. F. (2000). “Method of making damped composite structures with fiber wave patterns,” U.S. Pat. No. 6,048,426. US & PCT, Brigham Young University.    13. Pratt, W. F. (2000). “Crossply Wavy Composite Structures,” Provisional Patent Application 60/240,645. US & PCT.    14. Pratt, William. F; Allen, Matthew; Jensen, C. Greg, “Designing with Wavy Composites,” SAMPE Technical conference, 2001, Vol. 45, Book 1, pp 302-215.    15. Pratt, William. F; Allen, Matthew; Skousen, Troy S., “Highly Damped Lightweight Wavy Composites,” Air Force Technical Report AFRL-VS-TR-2001-tbd, 2001.    16. Reinfelder, W., C. Jones, et al. (1998). “Fiber reinforced composite spar for a rotary wing aircraft and method of manufacture thereof”, U.S. Pat. No. 5,755,558. US, Sikorsky Aircraft Corporation.    17. Sample, Joe M., “Break resistant ball bat,” 20001, U.S. Pat. No. 6,238,309.    18. Trego, A. (1997). “Modeling of Stress Coupled Passively Damped Composite Structures in Axial and Flexural Vibration,” Brigham Young University, Ph.D. Thesis, Provo, Utah, Brigham Young University.
Hyer (Reference 6) is a good all-around and current basic composite book that covers the properties of composites, especially unidirectional pre-preg based crossply laminates. Wavy composite is not mentioned at all.
Mellor (Reference 8) proposed the use of standard bi-directional cloth in a zig-zag (chevron) pattern contemplated by both Dolgin and Olcott as a constraining layer for viscoelastic materials. Mellor did not contemplate use of wavy or chevron patterned laminae used in conjunction with crossplies of unidirectional material that are substantially perpendicular to the general lay of the wavy or chevron patterned laminae. Nor did he discuss the use of woven fiber mats with wavy patterns in the warp, and/or such woven cloths with varying percentages of fill fibers.
Olcott (Reference 9) predated Mellor and proposed, fabricated, and tested the chevron patterns used as constraining layers for viscoelastic damping layers contemplated by Dolgin. Olcott did not contemplate use of wavy or chevron patterned laminae used in conjunction with crossplies of unidirectional material that are substantially perpendicular to the general lay of the wavy or chevron patterned laminae. Nor did he discuss the use of woven fiber mats with wavy patterns in the warp, and/or such woven cloths with varying percentages of fill fibers.
Reinfelder, et al, (Reference 16) discussed the construction of a rotary wing spar for use on a helicopter. It is a good example of the superiority of crossply laminates and is an example of an application that could benefit from the use of wavy crossply laminate structures.
Trego (Reference 18) extended the Finite Element Analysis model proposed by Olcott (Reference 9) and built several chevron based constrained layer damping tubes to validate the model. No mention was made of using wavy composites in wavy crossply lay-ups nor wavy or chevron patterned laminae used in conjunction with crossplies of unidirectional material that are substantially perpendicular to the general lay of the wavy or chevron patterned laminae. Nor did she discuss the use of woven fiber mats with wavy patterns in the warp, and/or such woven cloths with varying percentages of fill fibers.
Crossply lay-ups, as discussed by Reinfelder, et al, and Hyer, typically involve the use of unidirectional pre-preg with fiber orientations designed to maximize the desired structural properties. For example, if a tube is to be loaded in the longitudinal or axial mode, most if not all of the unidirectional fibers would be oriented in the longitudinal (or 0°) direction for maximum stiffness. Some small percentage of total fibers in the tube may be oriented perpendicular to these fibers for hoop strength, to prevent separation, or to prevent buckling, but such fibers would not resist longitudinal loads. Such tubes are easy to make by cutting an appropriate length of unidirectional pre-preg from a roll and rolling the composite onto a mandrel. No fibers (for the 0° layers) are cut or interrupted. Loads are resisted best when fibers are not cut. If cut, loads between such fibers are transmitted through the matrix or resin and stiffness and strength can be considerably reduced. A tube with all or mostly 0° fibers would be very efficient in resisting longitudinal loads but would not resist any significant torque or bending loads because such loads would be resisted primarily by the shear strength of the matrix and not by fibers.
A better design for resisting torque loads in a tube would be to add additional layers of fibers oriented at angles to the longitudinal axis so that the fibers would spiral around the tube. Such fibers would provide the primary resistance to torque loads and would provide resistance to shearing loads along the neutral axis during bending similar to a truss like structure. To avoid cutting the fibers (except at the ends of a tube) the unidirectional pre-preg would have to be spirally wound on the tube which is a concept that sounds simple, but in reality is extremely difficult to do correctly. More typically, the unidirectional materials are cut at an angle from a larger sheet and the “off-axis” rectangle of material thus created is rolled On to the tube as is done for the longitudinal fiber plies. This leaves a series of cut fibers that spiral around the tube ending on a discernable seam that runs the length of the tube. This represents a potentially significant weakness in the crossply laminate. If several such layers of opposing “off-axis” plies are used, the normal practice is to offset the ending and beginning of such plies so that the seams of each layer are offset. (Reinfelder, et al, 1998).
Pratt (Reference 10) proposed the use of wavy composite contemplated by Dolgin (references 3 and 4) as constraining layers for a soft viscoelastic damping material in several combinations of wavy composite, viscoelastic, and conventional materials. Additionally, Pratt proposed the use of “wavy pre-preg for use with or without a separate viscoelastic layer” but did not teach or further amplify the construction or benefits. Pratt (Reference 11, page 92) proposed, constructed, and tested balanced wavy composite crossply samples (without viscoelastic layers) for the purpose of determining the properties of wavy composite. Pratt (Reference 10) revealed and taught the advantages of using wavy crossply composite laminates in structures to provide improved structural properties, especially resistance to torque, bending, and axial loads.
Dolgin (Reference 3) proposed a specialty composite structure made from opposing chevron and sinusoidal patterned composite lamina constraining a viscoelastic layer. In Reference 4 Dolgin stated that the production of wavy sinusoidal pre-preg should be possible but did not describe any process or apparatus. Neither reference taught or cited any method of constructing or using wavy or chevron patterned composites as replacements for unidirectional pre-preg based wavy crossply laminates, nor the use of combinations of wavy crossply laminates in conjunction with Dolgin's (references 3 and 4) wavy damping methods.
Cabales, et. al. in references 1 and 2 propose the construction of golf club shafts using concepts invented by Dolgin (Reference 3) and techniques proposed by Olcott (Reference 9). The basic design contemplated by Cabales, et. al. relied on two load bearing laminates on the inside and outside of the shaft, placing a “damping device” in the space between these laminates using viscoelastic and “V” or “herringbone” fiber patterns proposed by Olcott (Reference 9). These V or herringbone patterns are constructed from strips of unidirectional material that is cut on an angle and then joined by a series of overlapping butt joints (Reference 9). Such methods are impractical in the extreme requiring an estimated 70 separate pieces of composite for one “damping device” that must be hand assembled for one shaft. Additionally, because of the inherent weakness of the overlapped butt joints, a minimum of four layers must be used for any V or herringbone damping layer (Reference 9). Such a shaft, if it can be accurately assembled at all, would weigh at least 50% more than a steel golf shaft and would therefore be unacceptable to the public. In short, such a design is impractical if not impossible.
Finally, Cabales, et. al. did not contemplate the use of wavy or sinuous fiber reinforced materials either in their claims or the disclosure of the invention but instead specifically cited Olcott's “V” or herringbone method in the claims. Additionally, Cabales, et. al. state that the use of precisely controlled regions or lengths of viscoelastic material application are required for the efficient damping of higher vibration modes of the shaft. More recent research in references 14 and 15 show that peak damping frequency and damping magnitude at any given frequency are only functions of the wave period and will dampen all modes based on the characteristics of the material.
Since Olcott did not use methods of testing that produce an accurate characterization or material nomograph of the “V”, herringbone, or “zig-zag” laminate design, such an understanding of the material's true properties was never accomplished and Olcott and others were left to erroneously conclude that damping performance was a function of the length of the damping regions and not a function of the period and maximum angle of the pattern.
Finally, Cabales et. al. indicate that the “V” or “herringbone”, or “zig-zag” patterns in the layers (items 10 & 12 in FIGS. 1-3, and items 310 & 312 in FIGS. 4-5) are joined along their length to the structural layers of the shaft (items 16 & 18 FIGS. 1-5) which defeats the differential shearing action necessary for damping. This means that these layers would be essentially non-functional and would contribute little if anything to the damping performance of the shaft. As shown by Pratt, et. al. in references 10, 14, and 15 wavy damping layers must be free to shear differentially to be effective. The same is true for the “V” or “herringbone”, or “zig-zag” patterns contemplated by Cabales, et. al.
In Reference 10, Pratt revealed an enhanced method of making composite structures with crossply characteristics but constructed entirely from wavy composite. Pratt showed how wavy composite pre-preg can be used to create virtually seamless crossply-like laminates with little or no interruption of fibers. Such a laminate displays the properties of both unidirectional and crossply characteristics in that it can efficiently resist both axial and transverse shearing loads.
Application of Dolgin's sinuous or wavy composite damping concept shown in FIG. 1 on a base structure made either with conventional composite materials (unidirectional, woven cloth), isotropic materials (steel, aluminum, etc.), or wavy crossply materials (FIG. 15, Item 7), provides for an efficient, lightweight, and highly damped golf club (FIG. 22) as one example. Such a golf shaft requires only 10 separate pieces of material including two viscoelastic layers, can be assembled in a few minutes and is capable of automated assembly, and is at least 25% lighter than a typical steel shaft of the same stiffness. Therefore there remains a need for a practical method of making golf club shafts (and other devices) using Dolgin's sinuous or wavy composite damping concept that has heretofore not been contemplated by others.
Easton, et. al. in Reference 5 describes an internally reinforced metal ball bat wherein the internal reinforcing material is comprised of bi-directional composite cloth layers applied to the interior of the barrel. The advantages cited were reinforcement, added strength and quicker shape recovery after impact. Lewark in Reference 7 reinforced a wooden bat in the handle region with bi-directional composite cloth layers to provide for breakage resistance. Sample in Reference 17 provided reinforcement to the handle of a wooden bat with straight fibers oriented along the length of the handle. None of these references mention wavy composite nor a method for reinforcing the handle of a bat with crossply wavy composite nor adding damping to the body of the bat using wavy composite damping layers. This is true for wooden bats, hollow metal bats, composite bats, or hybrid designs combining wood, and/or metal, and/or composite.
The composite structures of this invention may take a variety of forms, including plates with or without stiffeners, beams, curved surfaces, or irregular shapes. In any event, each structure has at least one wavy composite laminate and at least one viscoelastic layer. The viscoelastic layer need not be a separate material or layer but may be formed by a thin boundary layer of matrix from the composite during curing; such a wavy composite material would of course have a special matrix. This invention also includes the use of wavy laminates that have some substantially straight fibers arrayed generally perpendicular to the sinuous path of the wavy fibers for improved torsional, in-plane shear, and out-of-plane twisting resistance.